update sandbox-math.md

resource/locales/en_US/sandbox-math.md

@@ -4,7 +4,7 @@ See [MathJax](https://www.mathjax.org/).
 
 ## Inline Formula
 
-When $a \ne 0$, there are two solutions to \(ax^2 + bx + c = 0\) and they are
+When $a \ne 0$, there are two solutions to $ax^2 + bx + c = 0$ and they are
   $$x = {-b \pm \sqrt{b^2-4ac} \over 2a}.$$
 
 ## The Lorenz Equations

resource/locales/ja_JP/sandbox-math.md

@@ -4,7 +4,7 @@ See [MathJax](https://www.mathjax.org/).
 
 ## Inline Formula
 
-When $a \ne 0$, there are two solutions to \(ax^2 + bx + c = 0\) and they are
+When $a \ne 0$, there are two solutions to $ax^2 + bx + c = 0$ and they are
   $$x = {-b \pm \sqrt{b^2-4ac} \over 2a}.$$
 
 ## The Lorenz Equations

resource/locales/zh_CN/sandbox-math.md

@@ -4,7 +4,7 @@ See [MathJax](https://www.mathjax.org/).
 
 ## Inline Formula
 
-When $a \ne 0$, there are two solutions to \(ax^2 + bx + c = 0\) and they are
+When $a \ne 0$, there are two solutions to $ax^2 + bx + c = 0$ and they are
   $$x = {-b \pm \sqrt{b^2-4ac} \over 2a}.$$
 
 ## The Lorenz Equations